The most common and most likely answer to this crossword clue is the 6 letter word SEDATE
I've seen this crossword clue in Financial Times
S
E
D
A
T
E
More clues leading to the result SEDATE
- Staid, sitting down when the last one rises
- Composed a steed that's excited
- Solemn - is teased terribly
- Oddly, speedy anthem’s dull
- Pacify half-pissed female causing trouble
- Inwardly composed, at ease, calm
- Somewhat composed, at ease?
- Some losing heart on romantic assignation, lacking fire
- Some caused a terrifying calm
- Relax with partner after endless sex
Buddy explains!

The straight part
We know that "calm" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case calm = sedate.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does SEDATE mean?
SEDATE verb- To calm or put (a person) to sleep using a sedative drug.
- To make tranquil.
- (of a person or their behaviour) Remaining composed and dignified, and avoiding too much activity or excitement.
- (of an object, particularly a building) Not overly ornate or showy.